You need to get each photo down to about 140 kb or less (basically wakeworld size)

The export to email command in iphoto may not give you enough control to do that easily. I'd do a batch conversion in CS2 using your wakeworld settings, check the average size using the info command, and then attach a safe number of images to the email so Yahoo doesn't spit it back out at you.

Dropbox is a savior for me. Instead of resizing or degrading quality, just zip the files up and drop in a folder that stays in sync automatically. I always have large files i need to get people and that includes zipped up photos. It's free too. It just works so naturally you don't have to remember anything but putting something in a folder. Check it out by clicking the link below.

I didn't get in depth....but if you want to email someone....once its all synced up you can email the "public link" of the file. They click the link and it downloads the file. It's a really snazzy feature I use quite often.